A typical selective epitaxy process involves a deposition reaction and an etch reaction. The deposition reaction causes an epitaxial layer to be formed on monocrystalline surfaces of a substrate and a polycrystalline and/or amorphous layer to be formed on non-monocrystalline surfaces, for example, a patterned dielectric layer deposited atop the substrate. The etch reaction removes the epitaxial layer and the polycrystalline and/or amorphous layer at different rates, providing a net selective process that can result in deposition of an epitaxial material and limited, or no, deposition of polycrystalline material.
As the critical dimensions of devices continue to shrink, methods of selective epitaxial deposition, such as the exemplary method described above, require lower processing temperatures (e.g., about 600 degrees Celsius or less). Unfortunately, the inventors have observed that typical etching gases fail to provide a suitable selective window between the epitaxial layer and the polycrystalline and/or amorphous layer at such temperatures. While some etching gas mixtures have been discovered that can provide a suitable selective window, such gas mixtures operate at processing pressures substantially greater than the pressures used for the deposition reaction. Thus, process throughput is negatively affected due to disparity between processing pressures.